Apollodorus Library 2.1.4

[4]
  Reigning over the Egyptians Epaphus married Memphis, daughter of Nile, founded and named the city of Memphis after her, and begat a daughter Libya, after whom the region of Libya was called. ¹ Libya had by Poseidon twin sons, Agenor and Belus. ² Agenor departed to Phoenicia and reigned there, and there he became the ancestor of the great stock; hence we shall defer our account of him. ³ But Belus remained in Egypt, reigned over the country, and married Anchinoe, daughter of Nile, by whom he had twin sons, Egyptus and Danaus, ⁴ but according to Euripides, he had also Cepheus and Phineus. Danaus was settled by Belus in Libya, and Egyptus in Arabia; but Egyptus subjugated the country of the Melampods and named it Egypt < after himself>. Both had children by many wives; Egyptus had fifty sons, and Danaus fifty daughters. As they afterwards quarrelled concerning the kingdom, Danaus feared the sons of Egyptus, and by the advice of Athena he built a ship, being the first to do so, and having put his daughters on board he fled. And touching at Rhodes he set up the image of Lindian Athena. ⁵ Thence he came to Argos and the reigning king Gelanor surrendered the kingdom to him; ⁶ < and having made himself master of the country he named the inhabitants Danai after himself>. But the country being waterless, because Poseidon had dried up even the springs out of anger at Inachus for testifying that the land belonged to Hera, ⁷ Danaus sent his daughters to draw water. One of them, Amymone, in her search for water threw a dart at a deer and hit a sleeping satyr, and he, starting up, desired to force her; but Poseidon appearing on the scene, the satyr fled, and Amymone lay with Poseidon, and he revealed to her the springs at Lerna. ⁸